In recent years, trend towards more inexpensive video tape recorders is gaining momentum and there is a demand for reduction of running cost of a magnetic tape. However, commercially available elongation of recording period has so far advanced to mere recording modes capable of recording for periods two and three times that of a standard recording mode. Hereinafter, the recording modes capable of recording for periods two and three times that of the standard recording mode are, respectively, referred to as a "twofold recording mode" and a "threefold recording mode". Similarly, recording modes capable of recording for periods four, five and six times that of the standard recording mode are, respectively, referred to as a "fourfold recording mode", a "fivefold recording mode" and a "sixfold recording mode".
Hereinafter, a prior art video tape recorder is described. Conventionally, a video tape recorder which enables recording and playback in the sixfold recording mode as the long-time recording mode not less than five times the standard recording mode is known from Japanese Patent Laid-Open Publication No. 7-73405 (1995). This video tape recorder is shown in FIGS. 5 and 6. In FIGS. 5 and 6 which are schematically explanatory of arrangements of rotary heads of the conventional video tape recorder, small circles laid along a large circumference represent the mounted heads. In FIG. 5, there are provided a single head pair 5 (5R, 5L) for the standard recording mode having a head width slightly smaller than a double of a track pitch of the threefold recording mode, double azimuth type four heads constituted by a head pair 7 (7R, 7L) for the threefold recording mode having a head width substantially equal to the track pitch of the threefold recording mode and a head pair 6 (6R, 6L) for the sixfold recording mode having a head width slightly smaller than a double of a track pitch of the sixfold recording mode and an audio head pair 4 (4R, 4L) used in all the recording modes.
Hereinafter, functions of the conventional video tape recorder of the above described arrangement are described with reference to Japanese Patent Laid-Open Publication No. 7-73405 (1995). Initially, recording and playback in the standard recording mode and interchangeable playback in the threefold recording mode are performed by the single head pair 5. Meanwhile, recording and playback in the threefold recording mode are performed by the head pair 7, while recording and playback in the sixfold recording mode are performed by the head pair 6 for the sixfold recording mode, in which the track width is slightly smaller than the double of the track pitch of the sixfold recording mode and an azimuth angle is so set as to range from .+-.0.degree. to .+-.20.degree.. Special playback in the standard, threefold and sixfold recording modes is complemented by a digital circuit employing a field memory.
Then, the arrangement of the heads shown in FIG. 6 is described. In double azimuth type four heads 1R, 1L, 9R and 9L, the heads 1R and 1L form a head pair E used for recording and playback in the standard recording mode and the heads 9R and 9L form a head pair F used for recording and playback in the threefold recording mode. Generally, head widths of the head pairs E and F are so selected as to be about 49 .mu.m and 26 .mu.m, respectively. Meanwhile, the heads 8R and 8L are provided as a head pair G for recording and playback in the sixfold recording mode. A head width of the head pair G is set to be slightly smaller than a double of the track pitch of the sixfold recording mode. Furthermore, a head pair B constituted by the heads 4R and 4L is commonly used for high-fidelity audio recording and playback in the standard, threefold and sixfold recording modes. Generally, in view of interchangeable playback, a track width of the head pair B is so selected as to range from 26 .mu.m to 30 .mu.m. Interchangeable playback in the standard and threefold recording modes, recording and playback in the standard recording mode and special playback in both of the standard and threefold recording modes are performed by the head pairs E and F. Meanwhile, during ordinary playback of a track in the threefold recording mode, the head pair G is used such that crosstalk from an adjoining track of the track does not happen.
However, in the arrangement of FIG. 5, since during special playback in all the recording modes, it is necessary to provide a digital circuit having a field memory for storing in one field a video signal obtained by subjecting a playback signal output to FM demodulation and a color-under signal, such a drawback is incurred that the burden of cost is heavy as described in Japanese Patent Laid-Open Publication No. 7-73405 (1995).
Meanwhile, since the four heads including the heads having the azimuth angle different from that of prior art and the normal heads for the standard recording mode for the track pitch narrower than that of prior art should be produced additionally, such a problem will arise that the burden of cost is heavy also in view of balance between capital investment and the number of the heads to be produced.
Moreover, in the arrangement of FIG. 6, the head pair G for the sixfold recording mode is used as a playback head so as to prevent crosstalk during recording and playback in the threefold recording mode but disadvantageously yields an output lower than that of fulltrack playback.
Meanwhile, FIGS. 5 and 6 are common to each other in that recording and playback in the sixfold recording mode are exclusively performed by the heads having the head width slightly smaller than the double of the track pitch of the sixfold recording mode. Since recording and playback are performed by the same heads, such a contradiction is incurred that during recording, the head width should be larger than the track pitch such that an unerased portion of high-fidelity sound is eliminated, while during playback of a track, the head width should be smaller than the track pitch such that crosstalk from an adjoining track of the track is obviated. At the same time, such an inconvenience is also incurred that sound quality of high-fidelity audio is deteriorated extremely or allowance for interchangeable playback of high-fidelity audio signals in the standard or threefold recording mode is lessened excessively. This point is not referred to in Japanese Patent Laid-Open Publication No. 7-73405 (1995).
This point is explained in the sixfold recording mode with reference to FIG. 7. FIG. 7 is conceptually indicative of how the heads of the conventional video tape recorder trace recording tracks. P1, P2, P3 and P4 are tracks of high-fidelity sound and video signals in the sixfold recording mode and have a pitch of 9.6 .mu.m. The tracks P1 and P3 have an identical azimuth, while the tracks P2 and P4 have an identical azimuth.
The high-fidelity sound tracks and the video tracks do not necessarily coincide with each other but are here set to coincide with each other for simplification of the description. The head pair B is a high-fidelity head pair for performing recording and playback in the standard, threefold and sixfold recording modes and is composed of the heads 4L and 4R in FIGS. 5 and 6. Generally, in view of interchangeable playback, a head width of the head B is selected to range from 26 .mu.m to 30 .mu.m as described in Japanese Patent Laid-Open Publication No. 7-73405 (1995). Here, the head width of the head pair B is set at 26 .mu.m. The head pair G is a video head for recording and playback in the sixfold recording mode and is composed of the heads 6L and 6R in FIG. 5 and the heads 8L and 8R in FIG. 6. A head width Twg of the head pair G is set to be slightly smaller than the double of the track pitch of the sixfold recording mode, i.e., less than 19.2 .mu.m.
In FIG. 7, audio recording is performed by the head pair B. Since the head width of the head pair B is larger than the recording track pitch of 9.6 .mu.m of the sixfold recording mode, the head pair B is disposed relative to the recording tracks as shown in FIG. 7. Likewise, since the video signals are recorded by the head pair G having the head width larger than the track pitch, the head pair G is disposed relative to the recording tracks as shown in FIG. 7. Then, during playback, if the audio head pair B traces the track P4 having the azimuth identical with that of the track P2 when the head pair B traces the track P2, sound quality is deteriorated extremely and thus, the head pair B is controlled so as to be shifted to a position B', for example. The third track from the track P2 has an azimuth identical with that of the track P2 and is the track P4 in FIG. 7. Meanwhile, a track abutting on the track P2 is referred to as an adjoining track of the track. Adjoining tracks of the track P2 are the tracks P1 and P3. When the head pair B is controlled so as to be shifted to a position where a maximum allowance for preventing tracing of the third track from the track P2 is secured, namely, the head B is shifted from the recording position through 8.2 .mu.m (=(26-9.6)/2 .mu.m) such that a center of the track P2 coincides with a center of the head pair B, so that the position B' is obtained. As a result, influence of intense crosstalk from the third track P4 from the track P2 can be averted. However, when the head pair B is shifted through 8.2 .mu.m, the video head pair G is also shifted through 8.2 .mu.m. Since the head pair G is originally designed to trace the track P2, it becomes necessary to increase the head width of the head pair G by 8.2 .mu.m. Thus, the head pair G not only reproduces normal signals from the track P2 of 9.6 .mu.m in width but undergoes crosstalk from the track P1 through as long as 8.2 .mu.m. It follows that even the head pair 6 in which the azimuth angle has been changed is incapable of averting influence of deterioration of picture quality. On the contrary, if an attempt to prevent the head pair B from undergoing influence from the track P4 having the same azimuth as the track P2 is made by reducing the head width of the head pair B, it is difficult to guarantee interchangeability of FM sound in, especially, the standard recording mode.